An electrowetting display device, such as described in the international patent application WO 2003/071346, includes two support plates. A pattern of walls is arranged on one of the support plates, the pattern defining the picture elements of the display device. The area between the walls of a picture element, also known as a pixel, is called the display area, over which a display effect occurs. The walls of the picture elements are made of a hydrophilic material. The area of the support plate in the display area must to a large extent be hydrophobic for a proper operation of the picture element. During manufacture the area of the support plate where the picture elements are located is covered by a hydrophobic layer. The walls are made on this layer by depositing a layer of wall material onto the hydrophobic layer and patterning the layer of wall material using e.g. a photo-lithographic method.
The adhesion between the layer of wall material and the hydrophobic layer is relatively poor, causing easy peel off of the layer of wall material from the hydrophobic layer. It is known to lower the hydrophobicity of the hydrophobic layer prior to applying the layer of wall material by for example reactive ion etching. After the formation of the walls, the hydrophobic layer is annealed to regain its hydrophobicity. However, the quality of display devices made using this method is not satisfactory.
Other methods use a photo-lithographic step to lower the hydrophobicity only in a predetermined area by applying for example reactive ion etching, plasma or UV ozone treatment in the exposed area. Disadvantages are the requirement of an extra lithographic step and the difficulty of applying a lithographic process on a uniform hydrophobic surface with an increased risk of delamination.
It is an object of the invention to provide a method for making an electrowetting display device that does not have this disadvantage.